1. Field of the Invention
The present invention concerns polymer particles for use in toners usable for toners that are used in electrophotographic copying machines or printers and, more in particular, it relates to a method of manufacturing polymer particles for use in toners capable of preventing offset in heat fixing devices provided to copying machines or printers when used as toners, thereby capable of improving the fixing property and durability of the toners and capable of forming images at high fineness.
2. Description of Related Art
Toners used for copying machines or printers have been manufactured so far by a so-called pulverization method of melt kneading a colorant such as a carbon black or a pigment, additives, for example, a releasing agent such as wax and a binder resin by an extruder, followed by pulverization and classification. However, higher image quality has been demanded in recent years for copying machines and printers and, accordingly, it is demanded that the toner grain size is as small as 3 to 9 μm and the grain size distribution is also narrow. Attainment of such demands by the existent manufacturing method involves problems such as lowering of yield as the grain size is smaller.
Further, the toner particles obtained by the pulverization method involve a problem that their grain size distribution is wide although they are classified, and accordingly, the amount of static charges varies greatly due to the scattering of the grain size when individual toner particles are charged upon image formation. Further it also involves a problem of poor fluidity since the shape of the toner particles is indefinite.
On the other hand, a toner manufacturing method by a polymerization method has been known as a manufacturing method instead of the pulverization method in recent years. By the use of the method, a toner of a small grain size and a narrow grain size distribution can be obtained different from the pulverization method. The polymerization method includes emulsion polymerization, suspension polymerization, and dispersion polymerization, and the dispersion plymerization tends to be selected since spherical toners with narrow grain size distribution can be obtained easily.
As a method of manufacturing a toner using the dispersion polymerization method, Japanese Patent Laid-Open No. Hei 5(1993)-181315, for example, discloses a method of manufacturing a toner for development of static charge images formed by dying polymer resin particles obtained by adding and polymerizing vinyl monomers in a polymeric dispersant, adsorbing an emulsion wax at the surface of the obtained particles and further continuing polymerization. According to the toner manufacturing method described above, it is possible to manufacture a toner having excellent offset resistance in heat roll fixing and excellent in fluidity.
Further, Japanese Patent No. 2504745 describes a method of manufacturing an electrophotographic toner of dissolving or dispersing a radical polymerization monomer and a colorant in which an anti-offset agent such as various kinds of waxes is previously dissolved or dispersed into a reaction medium and polymerizing the radical polymerizable monomer under the presence of a radical initiator thereby obtaining a substantially spherical particle comprising a composition of the resin and the colorant. According to the manufacturing method described above, since the anti-offset agent is joined in a state dissolved or dispersed in a finely particulate state with the resultant polymer particle in the polymerizing reaction system, and the anti-offset agent is present as fine particles in the colored polymer particle, it is possible to manufacture a toner excellent in electrophotographic property as the toner.
However, in the toner manufacturing method described in Japanese Patent Laid-Open No. Hei 5(1993)-181315, the grain size of the polymer resin particles, and the addition amount of the wax have to be controlled strictly for uniformly depositing the wax particles on the surface of the polymer resin particle. Unless the control is conducted strictly, dispersed state of the wax in the mixed solution is instable and, as a result, the polymer resin particles tend to cause agglomeration to each other, so that the amount of the wax, if incorporated, in the polymer resin particle, is extremely small and not uniform.
Further, in the toner manufacturing method described in the U.S. Pat. No. 2,504,745, the amount of wax as the anti-offset agent that can be previously dissolved in the monomer is extremely small and since it is necessary to dissolve the wax into the monomer, the wax that can be used is restricted. Accordingly, the amount of the wax, if incorporated in the polymer resin particle constituting the toner, is extremely small.
As described above, in the toner manufactured by the dispersion polymerization method described in Japanese Patent Laid-Open No. Hei 5(1993)-181315 or Japanese Patent No. 2504745, only an extremely small amount of wax can be incorporated in the polymer resin particles. AS a result, when such polymer resin particles are used as the toner, they result in a problem that the mold releasing effect can not be provided sufficiently.
Therefore, in the printer using the toner described above, so-called heat-offset occurs during heat roller fixing and it is necessary to coat a releasing agent such as a silicone oil to a roller in order to prevent the heat offset. The coating of the releasing agent to the roller needs an additional coating device, which brings about a problem of increasing the cost of the printer main body.